1. Field of the Invention
The present invention relates to a method and an apparatus for measuring the hepatic blood flow amount. In particular, the present invention relates to a method and an apparatus for measuring the hepatic blood flow amount, which make it possible to easily measure the blood flow amount concerning the hepar (hereinafter simply referred to as the "liver" as well) by utilizing, for example, a xenon gas inhalator and an X-ray CT (computerized tomography) system.
2. Description of the Related Art
A method has been hitherto known, in order to measure the blood flow in the head of a patient. In this method, for example, a mixed gas of xenon gas and oxygen gas, which is fed from a gas inhalator, is allowed to be inhaled by the patient for a certain period of time by using a respiratory mask followed by allowing the patient to inhale normal air, while periodically obtaining tomographic images of the head of the patient as a specimen by using an X-ray CT system, to analyze the tomographic images so that the blood flow in the head of the patient is measured.
That is, according to the measuring method, the mixed gas passes through the lung of the patient, and it is absorbed into the pulmonary artery. The mixed gas passes through the heart, and it flows as an arterial blood flow into the tissue of the head. The mixed gas passes through the head tissue, and it is returned through the venous blood flow to the heart. The mixed gas passes through the heart, and it is returned to the pulmonary vein. During this process, the time-dependent change in xenon concentration in the head tissue is observed by using the X-ray CT system. The observed time-dependent change is compared with an authentic time-dependent change in xenon concentration in the head in which the tissue is normal. Thus, it is possible to diagnose the head of the patient.
The method for measuring the blood flow based on the use of the xenon gas as described above is not limited to the diagnosis of the head, and it can be also applied to normal organs (internal organs) such as the stomach, the intestine, and the pancreas in which arterial blood flow inflows thereinto and venous blood flow outflows therefrom as in the head.
However, when it is intended that the method for measuring the blood flow described above is applied to the liver, it is noted that not only arterial blood flow inflows into the liver. As disclosed in "EIZOJOHO MEDICAL" {issued in April 1994, Volume 26, Number 8, "Method for simultaneously measuring blood flows in hepatic artery and portal vein based on H.sub.2.sup.15 O intravenous injection method by using positron CT (about local blood flow amount difference in liver region)" (page 449 to page 453, Hiroki TANIGUCHI et al., the First Department of Surgery of Kyoto Prefectural University of Medicine) published by Industrial Development Organization (SANGYO KAIHATSUKIKO INC.) Co., Ltd.}, it is known that portal blood flow, as venous blood flow, which outflows from the stomach, the intestine, the pancreas, and the spleen as the portal internal organs, also inflows into the liver. Therefore, it is impossible to apply the foregoing conventional technique to the measurement of the blood flow amount in the liver.
A method for measuring blood flow amount in the liver is disclosed in "EIZOJOHO MEDICAL" described above. That is, a principle expression is introduced for the amount of blood which inflows and outflows with respect to the liver. The principle expression is solved on the basis of the result of measurement based on the H.sub.2.sup.15 O intravenous injection method by using the positron CT. Further, the liver is divided into four regions for each of which the total hepatic blood flow amount, the portal blood flow amount (total amount), and the hepatic arterial blood flow amount (total amount) can be measured, with respect to an injured liver and a non-injured liver.
However, in the case of the intravenous injection method based on the use of the positron CT, even when a blood flow image is obtained, it is still difficult to make comparison with an anatomical structure, and hence it is difficult to apply this method to image diagnosis.